1. Field of the Invention
This invention relates to a method of preheating an immersion nozzle for continuous casting.
2. Description of the Prior Art
As well known in the art, immersion nozzles for continuous casting are used under conditions so severe that they are required to have high spalling resistance. To meet the requirement, they are generally made of an appropriate combination of a fused silica-containing material, a graphite-alumina containing material, a silicon carbide-containing material, a zircon-containing material and a zirconia-containing material. Nozzles made of these materials must be heated thoroughly prior to their use. Preheating has conventionally been performed within an oven located far from the place of use. Gas has been a common medium for preheating but at least two hours are required to heat the nozzle to about 800.degree. C. Furthermore, so much time is involved removing the nozzle from the oven and installing it at a predetermined location that a temperature drop is inevitable in that interval. In addition, installing an object heated to high temperatures is difficult. What is more, if the temperature loss is excessive, cracking of the nozzle may occur or the deposit of inclusions such as Al.sub.2 O.sub.3 in the nozzle opening may render tapping impossible.